Combustible oxidizers are usually used as exothermic materials in smoking agents. The combustible oxidizers may also be used in pyrotechnics or as gas generators for automotive air bags.
As a conventional combustible oxidizer, potassium chlorate, potassium nitrate and the like have been mainly used. However, these combustible oxidizers are often highly sensitive to mechanical energy, i.e., energy generated by friction or shock. In particular, potassium chlorate has a high risk of exploding when handled, and hence, Japan Explosive Industry Association regulates its use.
Up to now, there has been no effective method developed for reducing the mechanical energy sensitivity of these combustible oxidizers. When such combustible oxidizers were used, there was no alternative but to handle them carefully.
Exothermic materials used in smoking agents have a risk of detonative reaction during their preparation or transport, since a combustible oxidizer and a fuel are mixed therein and are directly in contact with each other, which then can be easily ignited by mechanical energy such as friction or shock.
On the other hand, gas generators composed mainly of sodium azide are used in automotive air bags. However, with these, there are problems of the disposal of wastes containing sodium residue and the generation of toxic gas. Various efforts have been made to solve these problems; for example, a combination of tetrazoles with an oxidizer or a combination of azodicarbonamide (ADCA) with an oxidizer has been extensively studied as alternative materials to sodium azide.
Japanese patent laid-open publication Hei 3-242392 (1991) teaches a method for desensitizing an oxidizer highly sensitive to friction by forming a matrix with a polymer such as poly glycols. However, most of potential polymers for this invention have softening points of 100.degree. C. or less, and thus they are difficult to handle at an elevated temperature since their lower softening points lead to blocking in a dryer when oxidizers in a matrix are dried. Such polymer-matrix oxidizers have another problem in that they are less ignitable. This is because oxidizers dispersed in the polymer matrix cannot come in direct contact with fuel.
It is also kmown that some oxidizers such as potassium chlorate are unstable under acidic conditions, but no action has been taken to improve the stability of these oxidizers.
An object of the present invention is to provide an oxidizer less sensitive to mechanical energy and a method for reducing its mechanical energy sensitivity in order to make the handling easy and safe.
Another object of the present invention is to solve the problems of the above conventional oxidizers such as poor stability to heat or acids, and to solve the problems of the above conventional polymer-matrix oxidizers such as difficulties of handling them at an elevated temperature as well as poor ignitability.
A further object of the present invention is to provide a combustible composition having a low risk of, for example, detonative reaction.
A still further object of the present invention is to provide a gas generator for use in an air bag having a proper maximum pressure. Such air bag can then be produced at low cost.